Osage, IA has a population of 3,631 and is the 7,877th largest city in the United States. The population density is 1,601 per sq mi which is 2831% higher than the Iowa average and 1667% higher than the national average. The median age in Osage is 45 which is approximately 18% higher than the Iowa average of 38. In Osage, 63% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 77% of Osage residents were born in Iowa, 21% were born out of state, 1% were born outside of the United States and 0% were foreign born.